This invention relates generally to a liquid toner developer system in an electrophotographic printer and more particularly to a multi-purpose foam roller therein for removing excess liquid toner.
Electrophotographic printers or copiers using liquid toner have difficulty keeping the unit, and more particularly the photoconductor surface, free from excess liquid toner. Ideally, the liquid toner dispensal and development system is a closed loop system, with any excess toner not required by the image returned back to the system. Because of the properties of liquid toner, however, excess liquid toner can easily drip or run outside the ideal closed loop system.
The problems associated with excess liquid toner are particularly problematic in color printers and copiers where any excess liquid toner of any one color component, e.g., cyan, yellow, magenta, or black (CMYK), can adulterate the final image color. Controlling excess liquid toner in color printers and copiers is especially difficult where only a single developer station is used. If a single developer station is used, each individual color component is sequentially supplied to the developer station. Any residual amount of the previous color component that remains at the developer station mixes with the subsequent color component if not effectively removed.
One source of residual liquid toner is a "drip line" that forms between a photoconductor and a squeegee roller in a developer station. The squeegee roller, sometimes referred to as a "squeeze" roller, is placed downstream of a developer roller in contact with the photoconductor surface to remove any excess liquid from the photoconductor. An illustrative example of a developer station using a squeegee roller is shown in U.S. Pat. No. 4,801,965 issued to Mochizuki et al. Typically, the squeegee roller is rotatable in the same direction as the photoconductor to create a shear force therebetween. The shear force created by the squeegee roller "squeezes" out any excess liquid out of the liquid toner carried along the photoconductor surface. A buildup of the surface tension of the liquid results. This buildup, referred to herein as the "dripline," can remain even after the cessation of the toner supply.
The primary prior art method of removing excess toner does not address the drip-line. The primary cleaning as shown, for example, in Mochizuki, uses a foam roller downstream of the squeegee roller. The downstream foam roller does not address the drip-line, however. Similar approaches are taught in U.S. Pat. Nos. 4,905,047 and 4,627,705.
Accordingly, a need remains for a method of removing the drip line of liquid toner from an electrophotographic surface.